1. Field of the Invention
The present invention relates to a log processing system and, more particularly, to such a computer-based system which has the capability of processing dipmeter logs and conventional logs on the same system.
2. Setting of the Invention
In the exploration for oil and gas, various logs are obtained by passing a succession of tools through a wellbore traversing a subterranean formation. The logs are later processed or enhanced by using a programmable digital computer with one or more log processing software programs. Such logs include resistivity, gamma ray, permeability, water saturation, porosity, and the like, as is well known in the art. Another log which is often used is dipmeter log, which in essence is a microresistivity log. The dipmeter log is used to detect, identify, and analyze the various formations or beds below the earth's surface to determine the inclination of the formations, to identify faults, and to determine the position of the wellbore in relation to these features.
Since the dipmeter log is actually a microresistivity log, some resistivity logs and a dipmeter log obtained from the same formation and wellbore should be closely related, if allowance is made within the analysis for the physical natures of the different tools used and possibly for differences in data recording techniques. Often a resistivity log and a dipmeter log are not in agreement, and the only way to tell if the two logs were in agreement was to plot both logs on paper separately and then physically lay the dipmeter log alongside the resistivity log. A trained log analyst then has to determine if there is agreement between the two logs.
There is a need for a log analyst to be able, at one location and using a single computer-based system, to correlate dipmeter logs with other logs. There is a need for a system whereby the log analyst can evaluate information from other logs and from other sources, such as cores, and calculate results of other analyses concerning the conditions in the subterranean formation which might bear on the interpretation of the dipmeter data. Further, there is a need for a system that can allow the log analyst to re-examine the results of the other log analyses in light of the information from the dipmeter log. The inventor of the present invention knows of no such computer-based log processing system that has the capability to meet the above described needs.
Oftentimes, in obtaining the various logs, inaccurate data values occur, i.e., a resistivity measurement or a porosity measurement is either far less than or far more than what could even be conceivably possible for that particular formation. Also, oftentimes there are missing data points in the log. In each of these cases, the log analyst has to determine whether a new logging run must be made to obtain the data that is either in error or missing. While the log analyst is making this determination concerning the quality of the logging run, the operations at the well site have to stop until it is determined whether to re-log the well, complete the well, abandon the well, or drill further. Obviously, relogging of the well is extremely time consuming and very expensive. Having all work at the well site stop until completion of these analyses is even more expensive. There is a need for a single computer-based log processing system capable of reviewing log data, determining whether the data is acceptable, editing the log data to minimize additional processing runs, and conducting sufficient analyses to allow the user to determine what future course the drilling or well completion activity should take.
Oftentimes there is a need to analyze logging data obtained from previously drilled wells. While timely response is not as critical for this activity as for the activities previously described, the analysis and editing operation are of greater importance. Here the log analyst cannot simply order an additional logging run; after the decision concerning the fate of the well is made, the borehole is either lined with cement and steel or the well is plugged. In either case, additional logging runs are not possible. If the log analyst cannot find a particular log or the archival log is defective, there is need for a system capable of calculating the desired log values from other available logging data or substituting an acceptable log for the defective log. The results of these analyses lead to a more accurate knowledge of the subsurface geology and better direction of the exploration effort.
One log that can be used to calculate other log values is a dipmeter log. One of the primary problems encountered in trying to calculate other log values from a dipmeter log is that prior log processing systems treat the dipmeter log data totally differently than other logs, i.e., the dipmeter data is in a different format and is usually contained within different data bases. Therefore, prior log processing systems process dipmeter logs using a completely different set of log analysis or log processing software. Therefore, if the log analyst desires to use dipmeter data along with other conventional log data, then the log analyst has to use at least two different log processing systems and do some of the calculations by hand or visually by putting the logs together side-by-side. There is a need for a log processing system that can access differing data and oftentimes different formats in a timely fashion to allow the the dipmeter logs and the other conventional logs to be used in the same system. By treating the raw dipmeter logs and the results of the dipmeter analysis as the same kind of data as the conventional logging data, the log analyst can compare the results of different analyses with each other, can review the interpretation of the dipmeter log in light of the results obtained by the conventional logs, edit either for anomalous or invalid results, and perform these tasks in a sufficiently timely fashion to allow investigation of a variety of different hypotheses concerning the composition and slope of a formation. The inventor hereof knows of no such computer-based log processing system that has these capabilities.